zerofree finds the unallocated, blocks with non-zero value content in an ext2, ext3 or ext4 filesystem (e.g. /dev/sda1) and fills them with zeroes. This makes the disk easier to compress for Vagrant.

Login as root via VirtualBox. This will not not work when SSH'd into the machine because the command init 1 takes the system into single user mode. This means that services like sshd will be terminated.

Testing the new box

Create a directory for your vagrant file

$ mkdir -p ~/tmp/vagrant/env
$ cd ~/tmp/vagrant/env

Initialize your vagrant box

$ vagrant init vagrant-debian-wheezy
A `Vagrantfile` has been placed in this directory. You are now
ready to `vagrant up` your first virtual environment! Please read
the comments in the Vagrantfile as well as documentation on
`vagrantup.com`for more information on using Vagrant.

When done, you can "reset" the vagrant box with vagrant destroy. This will turn back the box to the default configuration you just set up during this tutorial. Everything you installed or configured in this machine after the vagrant up command will be lost forever.